1. Field of Invention
The invention relates to an antenna and, in particular, to a circuit-board antenna.
2. Related Art
Due to continuous development in communications technology, communication products are very common in daily life. Therefore, the demand for higher mobile communication quality becomes stronger. To obtain high-quality mobile communications, the antenna design in addition to better communication systems is also very important.
The conventional dipole antenna design is usually a xc2xd-wavelength (xcex) structure (see FIG. 1). In FIG. 2, however, the open end 11 of the signal part 10 in the dipole antenna is designed to be (1+xc2xc)xcex and the open end 21 of the ground end 20 is designed to be xc2xcxcex. The first radiation section 111 and the third radiation section 113 are radiating in the same direction, whereas the second radiation section 112 is radiating in the opposite direction, canceling with the radiation from the first and third radiation sections 111, 113. This changes the electromagnetic (EM) field shape of the antenna and therefore cannot increase its gain.
In this situation, increasing the length of the antenna is unable to effectively increase the gain. Therefore, existing dipole antennas are all designed in a symmetric way and the gain cannot be increased. However, for modern wireless communications, it is of great importance to enhance the antenna gain. How to extend the current antenna designs into those with higher gains has become a significant research field.
In view of the foregoing, it is an objective of the invention to provide a circuit-board antenna device, which has a higher radiation gain and adjusts to give better radiation orientation.
To achieve the above objective, the invention provides a circuit-board antenna, which can radiate and receive EM waves with a particular wavelength and is capable of increasing the radiation gain. The invention includes a circuit board, a signal part with an open end, and an open part with a ground. The circuit board has an upper surface and a lower surface. The signal part is formed on the upper surface of the circuit board. The open end is comprised of a plurality of radiation sections and a plurality of twisty sections. The path length of the open end is (n+xc2xc) times the particular wavelength, where n is a non-negative integer. Each of the twisty section is positioned between two of the radiation sections. The plurality of radiation sections are comprised of some radiation sections with a length of xc2xc times the particular wavelength while the rest with a length of xc2xd times the particular wavelength. The radiation sections are used to radiate and receive EM waves of the particular wavelength. The path length of each of the twisty sections is xc2xd times the particular wavelength so that the EM waves thus generated cancel with themselves. The open part is formed on the lower surface of the circuit board. The path length of the open part is xc2xc times the particular wavelength. Further scope of the applicability of the present invention will become apparent from the detailed description given hereinafter. However, it should be understood that the detailed description and specific examples, while indicating preferred embodiments of the invention, are given by way of illustration only, since various changes and modifications within the spirit and scope of the invention will become apparent to those skilled in the art from this detailed description.